Multimode wireless devices support more than one air-interface technology (e.g. GSM, cdma2000, UMTS etc.). Some air-interface technologies (such as cdma2000 release A, UMTS) support more than one concurrent service and provides users with more than one mode of operation such as simultaneous packet data session (e.g. email, browser) and voice.
There are three different classes of GSM/GPRS mobile stations. Class “A” mobile stations support simultaneous operation of GPRS and conventional GSM services. Therefore, class A mobile stations enable simultaneous support of a single circuit-switched session (e.g. voice) and one or more packet-switched sessions (e.g. e-mail). Class “B” mobile stations are able to register for both GPRS and conventional GSM services simultaneously; however, they can only use one of the two services at a given time. Therefore, class B mobile stations support either a circuit-switched session or a packet-switched session, but not both at the same time. Class “C” mobile stations can attach for either GPRS or conventional GSM services; however, with exception to SMS messages, simultaneous registration (and usage) is not possible. Therefore, class C mobile stations, much like class B mobile stations, support either a circuit-switched session or a packet-switched session, but not both at the same time. SMS messages can be exchanged over a circuit-switched session or a packet-switched session depending on network support. Some networks support exchange of SMS messages over only circuit-switched sessions while other networks support exchange of SMS messages over circuit-switched sessions and packet-switched sessions.
Similar class concepts exist in UMTS. GSM/GPRS mobile stations and network currently support only class B operation whereas in general all UMTS devices are considered class A. In release A of 1xEV-DO, multiple simultaneous packet services are supported, and different applications can have different QoS, each associated with the flow of the application. This allows multiple simultaneous asynchronous services such as a VoIP (Voice over IP) call along with other packet data services such as streaming video.